The present inventions are directed to methods and apparatus for operating a mobile unit more efficiently and linearly over a range of given RF signal output power levels.
In accordance with an aspect of the present inventions, the DC power consumed by a wireless communications mobile handset is regulated by transmitting an RF power output designating signal from a base station, wherein the RF power output designating signal indicates a desired power level of an RF signal output from the mobile handset. The RF power output designating signal is then received by the mobile handset, where it is used to set the level of the DC power provided to the mobile handset. Preferably, the level of the DC power is set to the minimum value necessary to maintain linear operation of an RF amplifier circuit contained within the mobile handset. The level of the DC power can be set by generating a control signal within the mobile handset. The level of the control signal is selected based on the RF power output designating signal. By way of non-limiting example, the control signal level can be selected from a plurality of control signal levels, wherein the control signals correspond to a respective plurality of RF power output levels. Thus, the control signal level corresponding to the RF power output level designated by the RF power output designating signal will be selected.
In accordance with a further aspect of the present invention, the DC power level is varied from the set DC power level in proportion to an envelope of the RF output signal. This can be accomplished by sensing the envelope of the RF output signal to produce a sampled envelope signal, which can then be added to the control signal.
In accordance with still a further aspect of the present inventions, a feedback loop, in conjunction with the control signal, can be used to set the level of the DC power. By way of non-limiting example, a supply current tracking signal, which indicates the present level of current supplied to an RF amplifier circuit contained in the mobile handset, is generated. The difference between the control signal and the supply current tracking signal is determined to obtain a biasing signal. The supply current, and thus the DC power supplied to the RF amplifier circuit, is then varied in proportion to the biasing signal. Alternatively, a supply voltage tracking signal, which indicates the present level of voltage supplied to the RF amplifier circuit, is generated. The difference between the control signal and the supply voltage tracking signal is determined to obtain the biasing signal. The supply voltage, and thus the DC power supplied to the RF amplifier circuit, is then varied in proportion to the biasing signal.
In accordance with still a further aspect of the present inventions, the RF power output designating signal indicates the existence of either a high RF output power condition or a low RF output power condition. The RF input signal is amplified through a driver. During a high RF output power condition, the DC power is provided to the RF amplifier circuit, and the RF signal is further amplified through the RF amplifier circuit. During a low RF output power condition, the flow of DC power to the RF amplifier circuit is impeded, and further amplification of the RF input signal is bypassed.
To further enhance the linearity and efficiency of the RF amplifier circuit, various features of the above-mentioned embodiments can be combined.
The present invention pertains to power amplifiers, including more specifically, a power amplifier circuit for wireless communication systems.
In wireless communication systems, mobile handsets communicate with other mobile handsets through base stations connected to the PSTN (public switched telephone network). Typically, in FDMA systems the base stations determine the frequencies at which the handsets are to communicate and send signals to the handsets to adjust the transmission power of the handsets.
The signals that are transmitted by the handsets are typically amplified prior to transmission to the base station. The amplification of the signal within the handset is generally performed by a radio frequency (RF) power amplifier 10, a representative embodiment of which is depicted in FIG. 1 (PRIOR ART). The RF power amplifier 10 includes a DC power terminal 12 and ground terminal 14. A DC power source 16 is typically connected between the power terminal 12 and the ground terminal 14, producing a supply voltage, VS, at the power terminal 12 and a supply current, IS, into the power terminal 12. Thus, the RF power amplifier is supplied with a DC power, PDC, equal to VS*IS. An RF input signal, RFin, generated by the transmitting handset, is fed into the RF power amplifier 10 via an RF input terminal 18. The RF power amplifier 10 amplifies the RF input signal, RFin, to produce an RF output signal, RFout, at an RF output terminal 20. The RF output signal, RFout, after passing through signal processing circuits, is typically sent to the antenna for transmission. An RF input signal, RFin, has an average input signal power, Pin, and an RF output signal, RFout, has an average output signal power, Pout.
When transmitting a signal with a non-constant envelope from a handset it is desirable to operate the power amplifier 10 in a linear mode to minimize signal distortion and bandwidth required to transmit the signal. The linearity of the power amplifier, which is measured by the uniformity of the transfer characteristic (Pout/Pin), varies with IS, VS, and RFout. Referring to FIG. 2 (PRIOR ART), the curves C1, C2, and C3 represent compression characteristics of an RF power amplifier 10 of FIG. 1, given three exemplary amplifier DC power, PDC, levels. The line L represents linear operation of the amplifier 10. As curves C1, C2, and C3 illustrate, the linearity of the power amplifier depends on PDC. That is, as PDC, increases, the range of Pin values for which the amplifier remains linear increases. In general, the output power, Pout, for which a power amplifier compresses increases with the DC power supplied to the power amplifier.
Although supplying a relatively high DC power to the RF power amplifier 10 will generally maintain linear operation of the RF power amplifier 10, such an arrangement becomes less advantageous in a system with varying transmission power requirements. A wireless communications system restricts the transmission power of the handset to minimize the signal from propagating to an excessively far point, so that the same frequency may be used at a far point, i.e., in other cells in order to permit servicing of as many subscribers as possible within the finite frequency resources allocated to the system. At the same time, the transmission power must be high enough to maintain the integrity of the transmitted signal over the distance that it travels to a base station. The magnitude of the handset transmission power required to maintain proper communication with a base station is dictated in part by the distance and the electrical communication environment between the handset and the base station. That is, if the handset is located far from a base station, the level of the RF output signal power, Pout, will be relatively high. If the handset is located close to the base station, the level of the RF output signal power, Pout, will be relatively low.
In a situation requiring a relatively low handset transmission power, an RF power amplifier that is supplied with a high DC power is inefficient. Referring to FIG. 1, the power the power amplifier 10 dissipates as heat is equal to the difference between the power supplied to the RF amplifier 10, PDC and Pin, and the RF output signal power, Pout, as characterized by the equation, PHEAT=PDC+Pinxe2x88x92Pout. Thus, given a constant DC supply power, PDC, the lower the RF output signal power, Pout, is, the more power the amplifier wastes as heat. The wasted power in the power amplifier 10 can be quantified in the power efficiency equation, Peff=Pout/(PDC+Pin). Thus, the more DC power that is supplied to an RF power amplifier, the less efficient that RF power amplifier becomes for a constant Pin and Pout.
Therefore, it can be understood that an RF power amplifier that is supplied with a relatively high constant DC power generally operates linearly over a full range of RF output signal, power levels, but is power inefficient, thus leading to significantly increased battery and heat sinking requirements, heavier battery weight, and shorter battery life. On the other hand, a power amplifier that is supplied with a relatively low constant DC power is power efficient, but generally operates only linearly over a low range of RF output signal power levels, thus resulting in a distorted transmission signal with a larger bandwidth.
There thus remains a need to operate a power amplifier more efficiently and linearly over a full range of given RF signal output power levels.
The present inventions solve this problem. The adaptable DC power consumption amplifier circuit of the present inventions include a control circuit such that an RF amplifier operates more efficiently and linearly over a full range of given RF signal output power levels.
In a preferred embodiment of the present inventions, there is provided an adaptable supply current circuit that maintains the supply current in an RF amplifier at a desired level. A supply current tracking signal indicative of the present level of the supply current, and a control signal indicative of the desired level of the supply current are generated. A biasing signal is generated based upon the difference between the control signal and the supply current tracking signal. The biasing signal is applied to the RF amplifier.
In another preferred embodiment of the present inventions, there is provided a dynamically adaptable supply current circuit that dynamically varies the supply current in RF amplifier from a desired level. A supply current tracking signal indicative of the present level of the supply current, and a control and envelope tracking signal indicative of the desired level of the supply current and the present level of a modulated RF output signal are generated. A dynamic biasing signal is generated based upon the difference between the control and envelope tracking signal and the supply current tracking signal. The dynamic biasing signal is applied to the RF amplifier.
To further enhance the linearity and efficiency of an RF amplifier, various features of the above-mentioned embodiments can be combined with features of other circuits disclosed in this specification, such as, e.g., an adaptable supply voltage circuit, a dynamically adaptable supply voltage circuit, or a bypassable circuit.